This invention relates to a pattern forming method by use of X-ray exposure, and more particularly to a pattern forming method which is capable of suppressing unnecessary exposure caused by secondary electrons or soft X-rays which are generated from a mask so that pattern contrast is improved.
As the integration level of semiconductor integrated circuits is increased, researchers have been paying attention to X-ray source as an exposure apparatus by which semiconductor integrated circuits are manufactured.
In X-ray lithography, development of resist materials which are used therefor have proceeded poorly since current resist materials are of low sensitivity. On the other hand, X-ray lithography has a problem in that pattern dimension is aggravated by dispersion of secondary electrons of X-ray.
FIG. 1 shows a conventional pattern forming method which uses conventional resist material. In FIG. 1A, substrate 1 is coated with resist 2 (e.g., CMS manufactured by Toyo Soda) by use of spin coating method. Then, in FIG. 1B, resist 2 is exposed to X-rays 4 selectively through mask 5. Thereafter, in FIG. 1C, development is carried out by use of a 1:1 mixture solution of isopropyl-alcohol and methyl-isobutyl-ketone to remove the unnecessary portion of resist 2 so that resist pattern 6 is formed.
In the FIG. 1B step, when X-rays 4 are applied to mask 5 which is made of, for example, Au, secondary electrons 7 are generated from mask 5. The secondary electrons 7 are, then, applied to resist 2 so that a part of resist to which secondary electrons 7 are exposed is sensitized. Therefore, resist pattern 6 which is obtained at the FIG. 1C step is different from pattern of mask 5. The secondary electrons 7 may be soft X-rays. Soft X-rays are generated when X-rays 4 are applied to mask 5.